Wavelength Division Multiplexing (WDM) has revolutionized the world of fiber optics by dramatically increasing the bandwidth of optical fiber. WDM enables a number of different wavelengths of light to be transmitted along an optical fiber, thus increasing the number of light signals that may be transmitted at the same time. For example, an ordinary, non-WDM system may only utilize light signals at a single wavelength, such as 700 nm. In contrast, a WDM system may utilize light signals at a variety of different wavelengths, such as 980 nm, 1330 nm, 1480 nm, 1530 nm, 1560 nm and 1650 nm. Thus, WDM systems can enable multiple light signals at different wavelengths to travel separately and simultaneously along an optical fiber.
Additionally, WDM systems often use WDM couplers to separate light signals traveling at different wavelengths along an optical fiber. This is often done at receiving ends of telecommunications systems, where light signals may be separated and channeled along different fibers to various destinations. For example, if an optical fiber carrying two light signals at different wavelengths is passed through a WDM coupler, the light signals may be separated and exit the coupler along two separate optical fibers. This separation may occur due to the fibers' indices of refraction as well as the orientation and location of the fibers with respect to each other. Thus, a WDM coupler may enable multiple light signals that are multiplexed together to be split, allowing a light signal traveling along one fiber to pass uninterrupted to another fiber.
In addition, a properly calibrated WDM coupler may be used to measure the wavelength of a light signal based on the coupler's inherent wavelength dependence. For example, suppose a WDM coupler is designed to send 50% of a 1530 nm wavelength light signal into a first fiber and 50% of the light signal into a second fiber, and the coupler has different splitting ratios for light signals at other wavelengths. Since the wavelength dependent splitting ratio of the coupler is known at 1530 nm, the coupler could be used to test if an incoming light signal has a 1530 nm mean wavelength. Generally, WDM couplers may be used to measure the wavelength of a light signal in applications such as fiber optic gyroscopes, where the wavelength of light exiting a fiber optic coil may be measured to see what deviations have been caused by the coil. These deviations may then be used to correct the output of the gyroscope by compensating for any variation in scale factor caused by a mean wavelength shift.
Unfortunately, however, existing embodiments of WDM couplers have certain limitations. For example, temperature variations can often alter the intrinsic characteristics of a WDM coupler. To illustrate, a temperature variation within a coupler may cause certain materials to expand or contract, which may result in a change in the length of the optical fibers within the coupler. Additionally, the temperature variation may also change the intrinsic effective index of refraction of the optical fibers. Both of these changes may shift the center wavelength in the coupler's splitting spectrum, thus changing its wavelength-dependent splitting ratio.
Therefore, existing WDM couplers may be vulnerable to temperature variations that degrade the performance of the WDM system. Accordingly, it is desirable to have a coupling device that overcomes the above deficiencies associated with the prior art.